File device and file access method

Abstract

The present invention relates to a file device and file access method that divides a file into units of clusters or blocks and records, and has as its object to provide a file device and file access method such that even when there is a failure and the data is not recorded correctly to the end the data that has been recorded can be accessed. When recording a file to an external storage device divided among a plurality of blocks, the blocks that are to record the file are pre-allocated in the external storage device, management information that indicates the allocated blocks is created and the management information is recorded in the external storage device, after which the data that makes up the file is recorded in the external storage device.

Description

[0001]This application is a continuing application filed under 35 U.S.C. § 111(a), based upon International Application PCT / JP99 / 04711, filed Aug. 31, 1999.TECHNICAL FIELD[0002]The present invention relates to a file device and file access method, and more particularly, to a file device and file access method that divides a file into units of clusters, blocks, or the like for recording and management.BACKGROUND ART[0003]Conventionally, OS (operating systems) such as MS-Windows and UNIX, when storing data to an external storage device, have stored connections of individual clusters, blocks or the like in management data called an FAT (File Allocation Table) and an index node (i-node).[0004]In such a system, when a file is read out, the clusters or blocks corresponding to that file are accessed in sequence while referring to the management information.[0005]Additionally, when storing a new file or when rewriting data, conventionally, clusters or blocks for storing the new data sequenc...

AI Technical Summary

Benefits of technology

[0037]According to the present invention, the blocks that are to record the file in the storage means are already allocated and the file is recorded after recording the management information that indicates the allocated blocks in the storage means, so even if a failure occurs during file storage there is no loss of management data, and accordingly, data already recorded in the file can be read out based on the management information.

[0039]According to the present invention, by attaching information indicating the preceding block and information indicating a size of data recorded in the block to data stored in each block, even when there is a disparity between the management data and the recorded data when reading out a file, confirming the preceding block and the size of the data recorded in the block makes it possible to identify valid data.

[0043]According to the present invention, by pre-setting a storage sequence of data that makes up the file and recording the data that makes up the file in blocks based on the set sequence, it is possible to access the file efficiently.

[0045]According to the present invention, by halting readout of a file and updating the management information so that subsequent blocks become unused blocks when information indicating the preceding block does not indicate the preceding block as a result of the block being accessed in sequence depending on the management information, the file being read out, and data being read out from the block, or when information indicating the size of the data recorded in the block is outside the actual block size range, it is possible to stop the readout of incorrect data and it is possible to update the management information so that the stored blocks of incorrect data become unused blocks. As a result, blocks can be used by other files and effective use can be made of the unrecorded blocks.

Problems solved by technology

When accessing the file, if the management information stored in the external storage device and the data sequence have been accessed alternately, a seek to the external storage device occurs for each access, which is inefficient.

However, in such a system, when recording data in the external storage device, in the event of a forced termination of the system, a system shutdown due to a power failure, or forced ejection of the removable storage medium when the external storage device is of the removal storage medium type and so forth, the management information that has been temporarily stored in the buffer is not recorded in the external storage device.

When the management information is not recorded in the external storage device and the file is accessed after restoration from any of the above-mentioned interruptions, because the management information has not been recorded a problem occurs in that the entire data recorded on the storage medium sequence cannot be read out.

It should be noted that if management information for the data sequence in the added storage cannot be stored due to a failure, then the data sequence in the added storage becomes invalid and a recovery process is carried out using the preceding data sequence.

However, according to the conventional USP method of (1), the existence of a storage medium capable of storing data even during a failure is required, and suffers the disadvantage of being unable to cope when removable media are forcibly removed.

If the blocks have been stored randomly, however, then a seek occurs each time an individual block is accessed, creating the problem of necessitating processing time.

As a result, random access occurs and disk access efficiency decreases.

Images